WO2016135489A1 - Substrat poreux hiérarchisé - Google Patents

Substrat poreux hiérarchisé Download PDF

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Publication number
WO2016135489A1
WO2016135489A1 PCT/GB2016/050477 GB2016050477W WO2016135489A1 WO 2016135489 A1 WO2016135489 A1 WO 2016135489A1 GB 2016050477 W GB2016050477 W GB 2016050477W WO 2016135489 A1 WO2016135489 A1 WO 2016135489A1
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Prior art keywords
porous network
substrate
functional sites
template particles
forming
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PCT/GB2016/050477
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English (en)
Inventor
Adam Fraser Lee
Christopher Michael Andrew PARLETT
Karen Wilson
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Aston University
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Application filed by Aston University filed Critical Aston University
Priority to GB1715449.3A priority Critical patent/GB2552911A/en
Publication of WO2016135489A1 publication Critical patent/WO2016135489A1/fr

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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
    • B01J20/103—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate comprising silica
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/02—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material
    • B01J20/10—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof comprising inorganic material comprising silica or silicate
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28088—Pore-size distribution
    • B01J20/28092—Bimodal, polymodal, different types of pores or different pore size distributions in different parts of the sorbent
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/28—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties
    • B01J20/28054—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof characterised by their form or physical properties characterised by their surface properties or porosity
    • B01J20/28095—Shape or type of pores, voids, channels, ducts
    • B01J20/28097—Shape or type of pores, voids, channels, ducts being coated, filled or plugged with specific compounds
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J20/00—Solid sorbent compositions or filter aid compositions; Sorbents for chromatography; Processes for preparing, regenerating or reactivating thereof
    • B01J20/30—Processes for preparing, regenerating, or reactivating
    • B01J20/305—Addition of material, later completely removed, e.g. as result of heat treatment, leaching or washing, e.g. for forming pores
    • B01J20/3057—Use of a templating or imprinting material ; filling pores of a substrate or matrix followed by the removal of the substrate or matrix
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/113—Silicon oxides; Hydrates thereof
    • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid

Definitions

  • the present invention relates to a porous substrate, for example, a porous substrate that may be used as a heterogeneous catalyst, a method of making such a porous substrate and uses of such porous substrates.
  • a substrate having a network of interconnecting pores As a heterogeneous catalyst for chemical reactions.
  • the porous substrates are formed using sol-gel condensation of the substrate material around an array of template particles and subsequent removal of the template particles.
  • the template particles are typically removed from the substrate by high temperature solvation (e.g. refluxing with solvent at 100 °C) or by calcination.
  • the pores remaining after the removal of the template particles may be treated to provide functional sites which can then act to catalyse a chemical reaction.
  • Use of beads of cross-linked polystyrene as template particles yields a substrate having a network of macropores (with a pore size greater than 50 nm and typically around 200-500nm).
  • surfactants or tri-block copolymers e.g. poloxamers as templates particles yields a substrate having a network of mesopores (with a pore size between 2-50 nm).
  • Substrates having interconnecting networks of macropores and mesopores are known and the larger macropores are considered to provide easier accessibility for the reactants to access the functionalised mesoporous network.
  • These substrates are formed using two different arrays of template particles e.g. an array of polystyrene beads (to form the macropores) and an array of liquid crystalline surfactant particles (to form the mesopores).
  • the template particles are removed simultaneously by calcination to leave interconnected networks of macropores and mesopores.
  • Macroporous-mesoporous alumina substrates are also known (Dacquin et al, J. Am. Chem. Soc. 2009, 131, 12896-12897).
  • a macroporous-mesoporous silica substrate carrying palladium nanoparticles for the selective oxidation of alcohols to yield commercially important cinnamaldehyde has also been described (Partlett et al., ACS Catal. 2013, 3, 2122-2129).
  • Multi-step reactions e.g. cascade reactions
  • a dual/multi-functionality substrate can be prepared by carrying out more than one functionalization treatment on the pores remaining after the removal of the template particles.
  • the two or more functional sites resulting from the multiple functionalization treatments are uniformly distributed throughout the porous network i.e. the differing functional sites are not spatially segregated within the substrate.
  • the present invention provides a method of producing a substrate comprising a porous network, said method comprising:
  • the first aspect of the present invention allows removal of template particles at sub-ambient temperatures unlike the known methods which require high temperature solvation or calcination. Such a method presents possibilities for the selective removal of template particles in situations where multiple arrays of differing template particles are provided as described in the second aspect of the present invention discussed below.
  • the high temperature methods of template particle removal previously used are aggressive and do not allow for selective template removal.
  • the temperature of the solvent used to remove the template particles may be at or below 0°C (e.g. at or below -5°C or -7°C).
  • the template particle is formed of a polymer.
  • the polymer may be an un-cross-linked polymer such as an un-cross-linked hydrophobic polymer or may be cross- linked.
  • the template particle may be formed of polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA) which may either be un-cross-linked or cross-linked.
  • polystyrene beads used as template particles in known methods are typically cross-linked and require meticulous preparation.
  • un-cross-linked polymers e.g. un-cross-linked polystyrene can be used in the present invention and the preparation of this does not need to be so accurately controlled.
  • the solvent used to remove the polystyrene template particles may be an aromatic solvent e.g. benzene, xylene, mesitylene or toluene. Toluene is preferred for cost and toxicity reasons.
  • the solvent used to remove the PLA template particles may be an organic solvent such as tetrahydrofuran (THF), a chlorinated organic solvent or acetonitrile.
  • the solvent used to remove the PMMA template particles may be an organic solvent such as methyl isobutyl ketone, methyl acetate or THF, or a binary solvent mixture such as acetonitrile/alcohol (e.g. methanol, ethanol or propanol).
  • the substrate and substrate precursor may be formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides.
  • Known methods can be used to form the substrate precursor.
  • the template particle array may be pre-formed and the substrate material formed around the template particle array using sol-gel synthesis or co- precipitation.
  • the method further comprises forming functional sites on the surface of the substrate within the porous network.
  • the functional sites may be formed by chemisorption (covalent, ionic, hydrogen), electrostatic physisorption or ligand exchange using various chemical species.
  • a precursor e.g. an alkoxy, halide or hydroxide precursor
  • the substrate can be used as a heterogeneous catalyst for a wide variety of chemical reactions.
  • the present invention provides a method of producing a substrate comprising a first porous network and a second porous network, the two porous networks being interconnected, said method comprising:
  • the first and second template particles have differing chemical and/or physical properties.
  • the first and second template particles may have differing sizes.
  • the first template particles may be larger than the second template particles, e.g. such that the first porous network comprises macropores and the second porous network comprises mesopores.
  • the macropores preferably have a size of 50 ⁇ -10 ⁇ as determined by mercury porosimetry or electron microscopy.
  • the mesopores preferably have a size of 2-50 nm and more preferably, 2.5-14 nm as determined by nitrogen physisorption and application of the BJH method to analysis of the corresponding isotherms.
  • the first and second template particles have differing thermostability. In some embodiments, the first and second template particles have differing polarity. In some embodiments, the first and second template particles have differing photochemistry. These chemical/physical differences can be used to facilitate selective removal of the first template particles.
  • the invention comprises using a solvent at a temperature below room temperature (e.g. at or below 0°C) to selectively remove the first template particles.
  • the temperature of the solvent used to remove the first template particles may be at or below -5°C (e.g. at or below -7°C).
  • the first template particle is formed of a polymer.
  • the polymer may be an un-cross-linked polymer such as an un-cross-linked hydrophobic polymer or may be cross- linked.
  • the template particle may be formed of polystyrene (PS), polylactic acid (PLA) or poly(methyl methacrylate) (PMMA) which may be either un-cross-linked or cross-linked.
  • the solvent used to remove the polystyrene template particles may be an aromatic solvent e.g. benzene, xylene, mesitylene or toluene. Toluene is preferred for cost and toxicity reasons.
  • the solvent used to remove the PLA template particles may be an organic solvent such as tetrahydrofuran (THF), a chlorinated organic solvent or acetonitrile.
  • the solvent used to remove the PMMA template particles may be an organic solvent such as methyl isobutyl ketone, methyl acetate or THF, or a binary solvent mixture such as acetonitrile/alcohol (e.g. methanol, ethanol or propanol).
  • the second template particles are formed of a surfactant.
  • the surfactant may be a non-ionic surfactant or may be a cationic surfactant such as cetyltrimethylammonium bromide (CTAB) or its derivatives (with differing length alkyl groups and/or differing counter ions).
  • CTAB cetyltrimethylammonium bromide
  • the second template particles are formed of a non-ionic block copolymer such as a poloxamer (e.g. Pluronic P123).
  • the second template particles are formed of a carboxylic acid.
  • the method comprises subsequently removing the second template particles using thermal processing (e.g. furnace or microwave irradiation), chemical extraction (optionally under thermal, microwave or ultrasonic conditions), chemical decomposition (e.g. using concentrated inorganic acid such as concentrated sulphuric acid) or UV/visible irradiation.
  • thermal processing e.g. furnace or microwave irradiation
  • chemical extraction optionally under thermal, microwave or ultrasonic conditions
  • chemical decomposition e.g. using concentrated inorganic acid such as concentrated sulphuric acid
  • UV/visible irradiation e.g. UV/visible irradiation
  • the method comprises subsequently removing the second template particles by solvation using a solvent at its reflux temperature e.g. at a temperature above room temperature (e.g. at or above 50°C or at or above 70°C).
  • the solvent may be a polar solvent such as an alcohol, e.g. a C1-C6 alcohol, namely methanol, ethanol, i-propanol, butanol, pentanol or hexanol.
  • a non-polar solvent such as toluene or xylene or a supercritical fluid such as carbon dioxide or water could also be used.
  • the method comprises forming first functional sites on the surface of the substrate within the first porous network and/or forming second functional sites on the surface of the substrate within the second porous network.
  • the surfaces within the first and/or second porous network may be functionalised by physisorption or chemisorption (covalent, ionic, hydrogen bonding) or ligand exchange at the surface hydroxyl groups within the first/second porous network.
  • a precursor e.g. an alkoxy, halide or hydroxide precursor
  • the surfaces within the first porous network are functionalised by covalent bonding.
  • the first and/or second functional sites may comprise a catalytic metal (e.g. platinum (Pt) or palladium (Pd)), a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group.
  • a catalytic metal e.g. platinum (Pt) or palladium (Pd)
  • a fluorescent marker e.g. an acidic group, a basic group, a hydrophilic group or a hydrophobic group.
  • the first/second functional site may comprise an enzyme or dye.
  • the first and second functional sites differ from one another and the first and second functional sites differ in functionality from one another.
  • the method comprises forming first functional sites on the surface of the first porous network before subsequently removing the second template particles from the substrate precursor. In this way, the first porous network will be functionalised whilst the second porous network remains unaffected.
  • the first functional sites are preferably covalently linked and, preferably, only decompose at elevated temperature (e.g. above ⁇ 250°C). Therefore they remain unaffected during the second template removal.
  • the method comprises forming second functional sites on the surface of the second porous network after subsequently removing the second template particles from the substrate precursor.
  • some embodiments provide a method of producing a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;
  • the first functional sites are selected to block subsequent functionalisation of the pores of the first porous network by the reagent used to form the second functional sites.
  • the first functional sites may occupy all available surface hydroxyl groups within the first porous network rendering it unsusceptible to further functionalisation, inaccessible, or the first functional sites may be selected to repel the reagent used to form the second functional sites.
  • the first functional site may comprise a hydrophobic functionality which forms strong covalent bonds with the hydroxyl groups on the surface of the first porous network and which also repels an aqueous reagent e.g. an aqueous metal (e.g. Pt) salt solution which is subsequently used to form catalytic metal (e.g. Pt) particles in the second porous network.
  • an aqueous reagent e.g. an aqueous metal (e.g. Pt) salt solution which is subsequently used to form catalytic metal (e.g. Pt) particles in the second porous network.
  • the hydrophobic functionality at the first functional site may comprise alkyl chains such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl.
  • the method may comprise forming the first functional sites on the surface of the first porous network by hydrolysis of alkylsilane precursors
  • Catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous h PtCk Chemical or photochemical reduction may be carried out to induce metal nanoparticle formation at the second functional sites, where reduction may be conducted at a low temperature (e.g. 25-100 °C).
  • aqueous platinum salt solution such as aqueous h PtCk Chemical or photochemical reduction may be carried out to induce metal nanoparticle formation at the second functional sites, where reduction may be conducted at a low temperature (e.g. 25-100 °C).
  • the step of forming the first functional sites comprises introducing a hydrophilic species (e.g. a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species).
  • the step of forming the second functional sites comprises introducing a hydrophobic species (e.g. a capped metal (e.g. Pt) nanoparticle).
  • a hydrophobic species e.g. a capped metal (e.g. Pt) nanoparticle.
  • the hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network.
  • a further hydrophilic species e.g. aqueous metal (e.g.
  • the functional sites may be selected such that they are too large to form in the smaller pores.
  • the first functional sites may comprise bulky hydrophobic or hydrophilic groups having a size too large to enter mesopores (e.g. in the second porous network) but which are able to enter macropores (e.g. in the first porous network.)
  • the first functional sites may further comprise a catalytic metal and may be formed from pre-formed metal containing particles e.g. Pd-containing nanoparticles which are too large to enter the mesopores.
  • a particularly preferred embodiment provides a method of producing a substrate comprising a first porous network having catalytic palladium sites and a second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising: forming a substrate precursor containing an array of first template particles and an array of second template particles;
  • the catalytic palladium sites can be introduced using preformed Pd nanoparticles. This allows their size to be controlled so that they are larger than the mesopore dimensions and thus cannot physically fit into them.
  • Suitable preformed nanoparticles are oleylamine capped Pd nanoparticles which may have a dimension of 5-50nm.
  • the capping agent imparts a hydrophobic character to the nanoparticles. Unstabilized Pd nanoparticles may also be used.
  • the catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous hkPtCk Metal reduction at low temperature (e.g. 25-100°C) may be carried out to induce metal nanoparticle formation.
  • aqueous platinum salt solution such as aqueous hkPtCk Metal reduction at low temperature (e.g. 25-100°C) may be carried out to induce metal nanoparticle formation.
  • a further preferred embodiment provides a method of producing a substrate comprising a first porous network having catalytic palladium sites and a second porous network having catalytic platinum sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:
  • the hydrophilic functional sites in the first porous network may be introduced using a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species.
  • the step of forming the second functional sites comprises introducing a hydrophobic capped Pt nanoparticle.
  • the hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network.
  • An aqueous Pd salt solution is then introduced to selectively enter the macropores (being too large to enter the mesopores and repelled from the mesopores by the hydrophobic Pt nanoparticles).
  • the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (e.g. Pt/Pd), an acidic group or a basic group.
  • the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.
  • the first functional sites comprise an acidic or basic functionality and the second functional sites comprise a catalytic metal.
  • the first functional sites comprise a catalytic metal and the second functional sites comprise an acidic or basic functionality.
  • the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality. In other preferred embodiments, the first functional sites comprise a basic functionality and the second functional sites comprise an acidic functionality.
  • the acidic functionality may be a Br0nsted acid functionality which may be introduced by using a thiolated organosilane precursor which can be subsequently oxidised to sulphonic acid.
  • the acidic functionality may be a Lewis acid functionality which may be introduced by using a metal alkoxide precursor which can be subsequently oxidised to a metal oxide (e.g. ZrC>2 or Ti0 2 ).
  • the acidic functionality may be a carboxylic acid functionality which may be introduced by using an organosilane with carboxylic acid groups or an organosilane precursor with nitrile groups that can be converted into carboxylic acid groups via acid or base hydrolysis.
  • the basic functionality may be an amine functionality which may be introduced by using an organosilane with amine functional groups, or an organosilane precursor with nitrile groups that can be converted into amine groups via reduction e.g. with UAIH4.
  • Enzyme functionality may be introduced by using an organosilane having carboxylic or amine functional groups and then hydrogen bonding or covalent bonding of amine or carboxylate functions within the enzyme to the organosilane carboxylate or amine functional groups.
  • the substrate and substrate precursor is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides.
  • Known methods can be used to form the substrate precursor.
  • the template particle arrays may be preformed and the substrate material formed around the template particle array using sol-gel synthesis.
  • the present invention provides a method of producing a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, the first porous network comprising macropores and the second porous network comprising mesopores, the two porous networks being interconnected, said method comprising:
  • the surfaces within the first and/or second porous network may be functionalised by physisorption or chemisorption (covalent, ionic, hydrogen bonding) or ligand exchange at the surface hydroxyl groups within the first/second porous network.
  • a precursor e.g. an alkoxy, halide or hydroxide precursor
  • the surfaces within the first porous network are functionalised by covalent bonding.
  • the step of forming the first functional sites comprises introducing a first functional species that is too large to enter the mesopores.
  • a first functional species that is too large to enter the mesopores.
  • preformed catalytic metal e.g. Pd
  • an enzyme or dye or a bulky hydrophilic species e.g. a polyalcohol or alcohol/carboxylic acid functionalised organosilane species or a bulky hydrophobic group such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl having a size larger than the size of the mesopores
  • a bulky hydrophilic species e.g. a polyalcohol or alcohol/carboxylic acid functionalised organosilane species or a bulky hydrophobic group such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl having a size larger
  • the first functional sites are selected to block subsequent functionalisation of the pores of the first porous network by the reagent used to form the second functional sites.
  • the first functional sites may occupy all available surface hydroxyl groups within the first porous network rendering it unsusceptible to further functionalisation, inaccessible, or the first functional sites may be selected to repel the reagent used to form the second functional sites.
  • the step of forming the first functional sites comprises introducing a hydrophobic species that is too large to enter the mesopores.
  • the step of forming the second functional sites comprises introducing a hydrophilic species (e.g. an aqueous metal (Pt) salt solution).
  • the hydrophobic species can bind to the surface hydroxyl groups in the first porous network. By binding to the surface hydroxyl groups, the hydrophobic species blocks the formation of any second functional sites within the first porous network.
  • the hydrophobic functionality at the first functional site may comprise alkyl chains such as alkyl chains containing 6 or more carbon atoms e.g. octyl chains or aromatic groups such as phenyl.
  • the method may comprise forming the first functional sites on the surface of the first porous network by hydrolysis of organosilane precursors
  • the step of forming the second functional sites comprises introducing an aqueous metal (e.g. Pt) salt solution into the second porous network.
  • the hydrophobic groups at the first functional site will repel the aqueous solution and the metal salt exclusively into the second porous network.
  • Catalytic platinum sites can be introduced using an aqueous platinum salt solution such as aqueous hkPtCk Metal reduction at low temperature (e.g. 25-100°C) is carried out to induce metal nanoparticle formation at the second functional sites.
  • Catalytic metal sites can then be introduced into the first porous network using pre-formed Pd nanoparticles which are too large to enter the mesopores.
  • the step of forming the first functional sites comprises introducing a hydrophilic species (e.g. a bulky polyalcohol or alcohol/carboxylic acid functionalised organosilane species) that is too large to enter the mesopores.
  • the step of forming the second functional sites comprises introducing a hydrophobic species (e.g. a capped metal (e.g. Pt) nanoparticle).
  • the hydrophilic groups at the first functional site will repel the Pt nanoparticles exclusively into the second porous network.
  • a further hydrophilic species e.g. aqueous metal (e.g. Pd) salt solution
  • the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (e.g. Pt/Pd), an acidic group or a basic group.
  • the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.
  • the first functional sites comprise an acidic or basic functionality and the second functional sites comprise a catalytic metal.
  • the first functional sites comprise a catalytic metal and the second functional sites comprise an acidic or basic functionality.
  • the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality.
  • the first functional sites comprise a basic functionality and the second functional sites comprise an acidic functionality.
  • the acidic functionality may be a Br0nsted acid functionality which may be introduced by using a thiolated organosilane precursor which can be subsequently oxidised to sulphonic acid.
  • the acidic functionality may be a Lewis acid functionality which may be introduced by using a metal alkoxide precursor which can be subsequently oxidised to a metal oxide (e.g. ZrC>2 or Ti0 2 ).
  • a metal alkoxide precursor which can be subsequently oxidised to a metal oxide (e.g. ZrC>2 or Ti0 2 ).
  • the acidic functionality may be a carboxylic acid functionality which may be introduced by using an organosilane with carboxylic acid groups or an organosilane precursor with nitrile groups that can be converted into carboxylic acid groups via acid or base hydrolysis.
  • the basic functionality may be an amine functionality which may be introduced by using an organosilane with amine functional groups, or an organosilane precursor with nitrile groups that can be converted into amine groups via reduction e.g. with UAIH4.
  • Enzyme functionality may be introduced by using an organosilane having carboxylic or amine functional groups and then hydrogen bonding or covalent bonding of amine or carboxylate functions within the enzyme to the organosilane carboxylate or amine functional groups.
  • the substrate and substrate precursor is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides.
  • Known methods can be used to form the substrate precursor.
  • the template particle arrays may be preformed and the substrate material formed around the template particle array using sol-gel synthesis.
  • the present invention provides a substrate comprising a first porous network having first functional sites and a second porous network having second functional sites, wherein the first and second functional sites are spatially separated/segregated and functionally/chemically different.
  • the pores in the first porous network are larger than the pores in the second porous network.
  • the first porous network may comprise macropores and the second porous network may comprise mesopores.
  • the first functional sites comprise a catalytic metal (e.g. Pt/Pd), an enzyme, a dye, a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group.
  • the second functional sites comprise a catalytic metal (Pt/Pd), a fluorescent marker, an acidic group, a basic group, a hydrophilic group or a hydrophobic group.
  • the first functional sites comprise an enzyme and the second functional sites comprise a catalytic metal (Pt/Pd), an acidic group or a basic group.
  • a substrate can be used to as a bio-chem catalyst to catalyse a multi-step reaction.
  • the first functional sites comprise a first fluorescent marker and the second functional sites comprise a second fluorescent marker.
  • a substrate could be used as a sensing device (e.g. protein sensing device) able to discriminate between the presence of multiple analytes on the basis of their size, for example enzymes such as myloperoxidase ( ⁇ 5 nm) and C-reactive protein (> 5 nm) in clinical applications.
  • the first functional sites comprise an acidic functionality and the second functional sites comprise a catalytic metal.
  • a substrate can be used as a catalyst for the conversion of glucose to sorbitol.
  • the first functional sites comprise Pd and the second functional sites comprise Pt.
  • Such a substrate can be used as a catalyst for selective oxidation of alcohols to acids e.g. cinnamyl alcohol to cinnamic acid (via cinnamaldehyde).
  • Cinnamic acid is an important flavorant and essential oil.
  • Pd is highly selective for catalyzing cinnamyl alcohol oxidation to cinnamaldehyde but promotes decarbonylation of the resultant aldehyde product.
  • Pt favours undesired hydrogenation of cinnamyl alcohol (via reactively-formed surface hydrogen) to 3-phenylpropionaldehyde, but is highly selective towards cinnamaldehyde oxidation to the desirable cinnamic acid product.
  • Embodiments of the present invention having Pd as the first functional sites and Pt as the second functional sites provide a catalyst design that ensures that cinnamyl alcohol is oxidized over Pd prior to encountering Pt sites, while permitting the reactively-formed cinnamaldehyde able to subsequently access Pt sites for the selective production of cinnamic acid in the second oxidation step.
  • Such a goal is achievable through the spatial control over the location of Pd and Pt within the substrate.
  • the first functional sites comprise an acidic functionality and the second functional sites comprise a basic functionality.
  • Such a substrate can be used as a catalyst for conversion of cellulose to hydroxymethylfurfural (HMF) or conversion of bio-oil to biodiesel, preventing subsequent poisoning of base sites required to catalyse oil component via transesterification.
  • HMF hydroxymethylfurfural
  • the substrate is formed of alumina, silica, a metal oxide such as zirconia, titania or ceria or mixed metal oxides.
  • Figures 1 A and 1 B show transmission electron microscopy images of the substrate precursor before ( Figure 1A) and after ( Figure 1 B) toluene extraction;
  • Figure 2 shows stacked nitrogen porosimetry isotherms of the substrate prior to extraction and after consecutive extractions of the first template particles;
  • Figure 3 shows surface area as a function of number of toluene extractions;
  • Figure 5 shows the nitrogen porosimetry isotherm of the substrate after octyl functionalisation
  • Figure 6 shows the nitrogen porosimetry isotherm of the substrate after extraction of the second template particles (P123) and mesopores size analysis
  • Figure 7 shows thermogravimetric analysis of the substrate prior to P123 template particle extraction (C8 functionalised) and after extraction of P123 template particles
  • Figures 8A and 8B show the water contact angle analysis of the octyl functionalised substrate post P123 template particle extraction (Fig 8A) and of a comparable material (Fig 8B) that has not been octyl functionalised;
  • Figures 9A and 9B show high resolution scanning transmission electron microscopy images, showing Pt nanoparticles within the mesopores of the substrate;
  • Figure 10 shows the particle size distribution for Pt nanoparticles
  • Figures 1 1A and 1 1 B show high resolution scanning transmission electron microscopy images of the substrate after introduction of Pd nanoparticles
  • Figure 12 shows the particle size distribution for Pt nanoparticles and Pd nanoparticles in the bimetallic substrate;
  • Figure 13 shows energy dispersive x-ray spectroscopy of areas of mesoporosity and macroporosity;
  • Figures 14A and 14B show cinnamyl alcohol conversions for the bimetallic substrate.
  • Figure 15 shows a comparison of cinnamyl alcohol conversion and cinnamaldehyde and cinnamic acid production for the bimetallic substrate with conventional substrates.
  • a substrate precursor comprising an array of first template particles comprising un-cross- linked polystyrene beads template particles and an array of second template particles comprising Pluronic P123 was formed.
  • the substrate precursor was synthesised via the methodology reported by Sen at al, Chemistry of Materials, 2004, 16, 2044-2054.
  • Styrene (105 cm 3 ) was washed five times with sodium hydroxide solution (0.1 M, 1 : 1 vol/vol) followed by five washings with distilled water (1 : 1 vol/vol) to remove polymerisation inhibitors.
  • the washed organic phase was added to nitrogen degassed water (850 cm 3 ) at 80°C followed by dropwise addition of aqueous potassium persulfate solution (0.24M, 50 cm 3 ) with 300 rpm agitation.
  • the reaction proceeded for 22 h, after which the solution had turned white due to the formation of polystyrene nanospheres. Solid product was recovered and colloidal crystal arrangement induced by centrifugation (8000 rpm, 1 h).
  • the resulting highly ordered polystyrene colloidal nanosphere crystalline matrix was finally ground to a fine powder for use as the first template particles.
  • Pluronic P123 (2 g) was sonicated with hydrochloric acid acidified water (pH 2, 2 g) at 40°C to a homogeneous gel.
  • the first template particles were removed by placing 10g of substrate precursor in 100ml of toluene at -8°C for 1 minute under high speed agitation at speeds above 600 rpm. The solid was recovered by vacuum filtration and washed with cold toluene. The extraction was subsequently repeated four times to fully extract the polystyrene template particles.
  • Figures 1A and 1 B show transmission electron microscopy images of the substrate precursor before ( Figure 1A) and after ( Figure 1 B) toluene extraction. It can be seen that a first porous network comprising macropores having an average size of 400 nm was generated. The Pluronic 123 template particles remained intact within the substrate precursor. This was confirmed by nitrogen porosimetry, thermogravimetric analysis (TGA) and gel permeation chromatography (GPC).
  • TGA thermogravimetric analysis
  • GPC gel permeation chromatography
  • Nitrogen porosimetry was undertaken on a Quantachrome Autosorb IQTPX porosimeter with analysis using ASiQwin v3.01 software. Samples were degassed at 150°C for 12 h prior to recording ISh adsorption/desorption isotherms. BET surface areas were calculated over the relative pressure range 0.02-0.2. Mesopore properties were calculated applying the BJH method to the desorption isotherm for relative pressures >0.35, and fitting of isotherms to the relevant DFT kernel within the software package.Thermogravimetric analysis (TGA) was conducted using a Stanton Redcroft STA 780 thermal analyser at 10°Cmin- 1 under flowing N 2 /0 2 (80:20 v/v 20 cm 3 min- 1 ).
  • Figure 2 shows stacked nitrogen porosimetry isotherms of the substrate prior to extraction and after consecutive extractions of the first template particles showing generation of macroporosity (sharp increase in volume at high relative pressure -0.95) and absence of mesoporosity (no increase in volume over the relative pressure range of 0.3-0.9) i.e. no extraction of second template particles (Pluronic P123).
  • Figure 3 shows surface area as a function of number of extractions showing an increasing surface area with extraction up to a maximum after four extractions, due to removal of the first template particles from the macropores, and a subsequent plateau due to complete extraction of the first template particles with no subsequent extraction of the second template particles.
  • Figure 4 shows the results of thermogravimetric analysis showing the levels of the first and second template particles remaining in the material after consecutive extractions of the first template particles. Extraction of the first template particles increased up to four extractions with levels of the second template particles unaffected.
  • the macropores in the first porous network were functionalised with octyl groups at the first functional sites by either refluxing an organosilane precursor in heptane solvent overnight, or room temperature wet impregnation with the organosilane precursor.
  • 2g of the substrate precursor was stirred in 6cm 3 of triethoxy(octyl)silane for 3 minutes and recovered by vacuum filtration before drying overnight at room temperature.
  • Figure 5 shows the nitrogen porosimetry isotherm of the substrate after octyl functionalisation which is comparable to that obtained prior to octyl functionalisation with no degree of mesoporosity from P123 template particle removal showing that P123 template particles remained within the substrate during the functionalisation of the first porous network.
  • a surface area of 19 m 3 g _ concurs with the parent material.
  • FIG. 6 shows the nitrogen porosimetry isotherm of the substrate after extraction of the second template particles (P123) and shows increased volume of nitrogen absorbed due to increased surface area (up to 300 m 2 g _ ) which results from mesopore evacuation, via P123 removal, which is evident from the type IV isotherm shape.
  • Mesopore size analysis using the BJH methodology (insert), reveals average mesopore diameter of 3.5 nm.
  • Figure 7 shows thermogravimetric analysis of the substrate prior to P123 template particle extraction (C8 functionalised) and after extraction of P123 template particles. The mass loss for material prior to extraction, at ⁇ 190°C is due to combustion of P123 with this feature absent in the extracted material, confirming removal of the P123 template particles.
  • Figures 8A and 8B show the water contact angle analysis of the octyl functionalised substrate post P123 template particle extraction (Fig 8A) and of a comparable material (Fig 8B) that has not been octyl functionalised and where the first and second template particles have be extracted under identical conditions.
  • the platinum nanoparticles were driven selectively into the mesopores since the hydrophobic groups in the macropores repelled the aqueous solution.
  • a dry porwder was obtained by gentle heating of the slurry at 50oC for 10 hours followed by low temperature (100 °C) metal reduction under H2 (10 cm 3 min- 1 ) for one hour to leave Pt particles having an average diameter of 2.2 nm within the mesopores. A Pt loading of 0.73 wt% was observed.
  • FIGs 9A and 9B show high resolution scanning transmission electron microscopy images
  • Pt nanoparticles appears as bright spots
  • Fig 9B Pt nanoparticles appear as black sports showing Pt nanoparticles within the mesopores of the substrate.
  • High resolution scanning transmission electron microscopy (S)TEM images were recorded on either a FEI Tecnai F20 FEG TEM operating at 200 kV equipped with an Oxford Instruments X-Max SDD EDX detector (1 Onm diameter spot-size) or a JEOL 21 OOF FEG STEM operating at 200keV and equipped with a spherical aberration probe corrector (CEOS GmbH) and a Bruker XFIash 5030 EDX.
  • Figure 10 shows the particle size distribution for Pt nanoparticles highlighting that ⁇ 98 % particles are smaller than the average mesopore size and are thus able to fit within the second pore network of the substrate.
  • the Pd content of this nanoparticle solution was determined by ICP-OES to be 11.0 ⁇ 0.12 mg (in 30cm 3 ), indicating around 43 % of the initial Pd is present in the nanoparticles after purification.
  • the as-prepared nanoparticles were characterised by TEM by casting one droplet of nanoparticle solution onto a holey carbon coated copper grid (Agar Scientific) and evaporation to dryness.
  • TEM imaging was performed using a JEOL 2100F FEG TEM with a Schottky field emission source, equipped with an Oxford INCAx-sight Si(Li) detector for energy dispersive spectroscopy.
  • the accelerating voltage was 200 kV.
  • the particle size distribution was obtained from imaging 6 different areas of the grid and measuring the diameter over 800 individual nanoparticles. No variation in particle size was apparent in different regions of the grid.
  • the substrate (0.3g) was treated with 6.5cm 3 of a 1 wt% heptane solution of the preformed oleylamine capped palladium nanoparticles.
  • the size of the pre-formed nanoparticles was larger than the average mesopore size.
  • FIGs 1 1A and 1 1 B show high resolution scanning transmission electron microscopy images of the substrate after introduction of Pd nanoparticles. In the bright field (Fig 11 A) and dark field (Fig 1 1 B) larger Pd nanoparticlesare shown within the macropores of the substrate. The presence of Pt within the mesopores is also viable, as these are deposited prior to Pd deposition. Using dark field configurations it is possible to distinguish between Pd and Pt due to the atomic number contrast nature of the technique which results in Pt appear brighter than Pd, (highlighted in Fig 11 B).
  • Figure 12 shows the particle size distribution for Pt nanoparticles and Pd nanoparticles in the bimetallic substrate, compared to equivalent monometallic materials. These show that size is unaffected by the presence of both metals, with the average size of the Pt particles being smaller than the average diameter of the second pore structure whereas the size of the Pd nanoparticles is larger than the second pore structure.
  • Figure 13 shows energy dispersive x-ray spectroscopy of areas of mesoporosity and macroporosity further showing the precise location of the Pd and Pt nanoparticles. Areas of secondary porosity (mesoporosity), where silicon (Si) and oxygen (O) are strongest also show presence of discrete Pt sites and absence of Pd, whereas first porosity (macropore) regions show reduced silica and oxygen levels, due to large emptiness, and show levels of Pd and the absence of Pt.
  • the dual-functionalised substrate was used as a catalyst in the selective oxidation of cinnamyl alcohol to cinnamic acid at 150 °C with 5 bar O2.
  • the catalytic selective oxidations were performed in a 100 cm 3 Buchi miniclave stirred batch reactor on a 75 cm 3 scale at 150 °C. 12.5 mg of catalyst was added to reaction mixtures containing 4.2 mmol cinnamyl alcohol (0.562 g), an internal standard (mesitylene, 0.1 cm 3 ), and toluene solvent (75 cm 3 ) at 150°C under 5 bar oxygen and stirring. Reactions were periodically sampled for off-line gas chromatography analysis via a Varian 3800GC with 8400 autosampler fitted with a CP-SN5 CB column (15m x 0.25mm x 0.25 ⁇ ). Conversion, selectivity and yields were calculated via calibration to reference compounds and quoted ⁇ 2 %.
  • the Pd catalytic sites will catalyse the conversion to the aldehyde - the alcohol will achieve good exposure to the Pd catalyst as a result of the large pore size in the first porous network.
  • the Pt catalyst site will then catalyse oxygen insertion into the C-H of the aldehyde forming the acid.
  • Figures 14A and 14B show cinnamyl alcohol conversions for the bimetallic substrate are comparable to both monometallic substrates, Pd in macropores or Pt in mesopores ( Figure 14A).
  • the true benefit of the bimetallic system is apparent when cinnamic acid yield ( Figure 14B), the desired product from consecutive oxidations, is evaluated with a 10 fold increase in productive for the bimetallic substrate over either of the monometallic substrates.
  • Figure 15 also shows a comparison of cinnamyl alcohol conversion and cinnamaldehyde and cinnamic acid production for the inventive bimetallic substrate (with spatially segregated Pd/Pt sites) with conventional monometallic catalysts, their combination as a physical mixture and conventional bimetallic substrates (with co-localised, un-segregated Pd/Pt sites).
  • the conventional substrates proved ineffective, with either low rates of alcohol oxidation, poor selectivity to the cinnamaldehyde intermediate and/or very poor acid production, demonstrating the inability of Pd or Pt to either individually catalyze the multi-step, cascade reaction, or to communicate effectively when isolated in discrete catalyst support particles.

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Abstract

La présente invention concerne un procédé de production d'un substrat comprenant un réseau poreux. Le procédé comprend la formation d'un précurseur de substrat contenant un réseau de particules de matrice ; et l'élimination des particules de matrice du précurseur de substrat à l'aide d'un solvant à une température inférieure à la température ambiante pour obtenir le substrat. Un procédé de production d'un substrat comprenant un premier réseau poreux et un second réseau poreux, les deux réseaux poreux étant interconnectés, est en outre décrit, ledit procédé comprenant : la formation d'un précurseur de substrat contenant un réseau de premières particules de matrice et un réseau de secondes particules de matrice ; l'élimination sélective des premières particules de matrice du précurseur de substrat pour former le premier réseau poreux ; et l'élimination ultérieure des secondes particules de matrice du précurseur de substrat pour former le second réseau poreux.
PCT/GB2016/050477 2015-02-25 2016-02-25 Substrat poreux hiérarchisé WO2016135489A1 (fr)

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CN106975473A (zh) * 2017-05-27 2017-07-25 苏州思美特表面材料科技有限公司 网络结构的负载型材料催化剂
US11680908B2 (en) 2017-10-06 2023-06-20 Corning Incorporated Assembly having nanoporous surface layer with hydrophobic layer

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WO2003064322A1 (fr) * 2002-01-29 2003-08-07 Imperial Chemical Industries Plc Materiaux siliceux comportant des mesopores et des macropores

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WO2003064322A1 (fr) * 2002-01-29 2003-08-07 Imperial Chemical Industries Plc Materiaux siliceux comportant des mesopores et des macropores

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LEBEAU B ET AL: "Synthesis of hierarchically ordered dye-functionalised mesoporous silica with macroporous architecture by dual templating", JOURNAL OF MATERIALS CHEMISTRY, ROYAL SOCIETY OF CHEMISTRY, GB, vol. 10, no. 9, 25 August 2000 (2000-08-25), pages 2105 - 2108, XP002243603, ISSN: 0959-9428, DOI: 10.1039/B003796F *

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN106975473A (zh) * 2017-05-27 2017-07-25 苏州思美特表面材料科技有限公司 网络结构的负载型材料催化剂
CN106975473B (zh) * 2017-05-27 2020-07-10 苏州思美特表面材料科技有限公司 网络结构的负载型材料催化剂
US11680908B2 (en) 2017-10-06 2023-06-20 Corning Incorporated Assembly having nanoporous surface layer with hydrophobic layer

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